Multi-cavity magnetron



July 9 1957 Filed Nov; 29, 1952 J. 5. DONAL, JR

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ATTORNEY United States Patent F MULTI-AV1TY MAGNETRON John S. Donal, Lin, Princeton, N. 5., assignor to Radio Corporation of America, a corporation of Deiaware Application November 29, 1952, Serial No. 323,277

8 Claims. (Cl. 250-436) My present invention relates to multi-cavity magnetrons and particularly to the anode of magnetron devices.

In view of the high frequencies at which magnetrons operate, the electrodes thereof, in particular the anode, form a substantial portion of the radio frequency circuit. As a consequence magnetrons made in the customary manner are seriously limited in their usefulness because of the relatively narrow radio frequency band width over which they may be operated. In most conventional structures the resonant cavities are included within the evacuated portion of the envelope. While such cavities may be tuned to some extent, any given envelope structure or tube is limited to a particular narrow band width. In BritishPatent 665,470, published on January 23, 1952, there is shown a magnetron in which the vanes of the anode structure are sealed through the envelope and which may effect substantial cost reduction as pointed out therein but which is not suitable for operation over such a broad band of radio frequencies as a device constructed in accordance with my present invention.

' It is therefore a principal object of my invention to provide a multi-cavity magnetron adapted for use over a radio frequency band width substantially broader than heretofore contemplated for such devices.

Another object is the provision of a magnetron envelope containing substantially only the interaction region of the device which may be used in operation with resonant circuits having widely different resonant frequencies.

In accordance with my invention I provide a multicavity magnetron in which the evacuated envelope contains merely the interaction region While the anode resonant structure is completed outside the enevelope. The anode elements are sealed through the envelope with the seal between the elements being located closely adjacent to the inner edges of the elements. Outside of the envelope the elements are preferably terminated substantially flush with the envelope with just enough of the elements projecting to make edge to edge contact with corresponding extension vanes of a resonant structure with which the device is to operate.

Further objects will be apparent as the nature of my invention is more fully understood from the following description taken in conjunction with the accompanying drawings wherein:

Figure 1 is a sectional view of a multi-cavity magnetron constructed in accordance with my invention;

Figure 2 is a sectional view along the line 22 of Figure 1;

Figure 3 is a sectional view of another device constructed in accordance with my invention;

Figure 4 is a sectional view of still another device constructed in accordance with my invention.

Referring now to the drawings in detail, the multicavity magnetron shown in Figures 1 and 2 comprises a unitary envelope portion indicated generally at 1th and may be for convenience designated as a capsule or tube. Tube comprises an indirectly heated cathode 11 with a heater Patented July 9, Z

mounted internally; lead 12 being one of the heater leads. If desired, the inner or free end of the cathode may be supported in the well known manner by joining the same to the adjacent wall. The cathode 11 is sealed through a central opening in end wall 13 as at 14. A tubular insulating member 15, preferably of ceramic material, is joined to end wall 13 at one end and at the other end is closed by end wall 16. End walls 13, 16 are conveniently pole pieces forming magnetic circuit elements. The connections of tubular member 15 to each of the pole pieces 13, 16 are each made in a vacuum tight manner as is well known.

A plurality of anode elements or vanes 17 are sealed along their length through envelope member 15. As is most clearly shown in Figure 2, vanes 17 are annularly spaced an equal distance apart one from the other radiating about a central axis which coincides with the axis of cathode 11. Each of the vanes 17 is held rigidly in place by the seal formed with member 15. Thus, end walls 13, 16, envelope member 15, cathode 11, and seal 14 form a unitary evacuated structure which forms the interaction region of the device.

I preferably accomplish strapping of the vanes 17 outside of the vacuum envelope to keep alternate vanes in phase. For this purpose, two concentric strapping rings 17a and 17b are provided at one or both ends of the vanes 17, with one ring 17a connected to alternate vanes 17 and the other ring 17b connected to the remaining vanes 17 as shown in Figures 1 and 2.

The resonant system is completed when capsule or tube 10 is inserted in a resonant circuit 18 which includes conductive wall members 19, 20, 21, which serve as the top, side, and bottom walls respectively. Top wall 19 is conveniently in the form of a thin flexible diaphragm and carries suspended therefrom tuner 221. As viewed in Figure 1, vertical movement of wall 19 is transmitted to tuner 22 to vary the effective strap capacitance and hence the frequency of operation. Connected to the inner surface of wall 29 and extending inwardly toward the axis of cathode 11 are a plurality of extension vanes 22. The inner edges of vanes 22 are angularly oriented and spaced to come into snug edge to edge engagement with the outer edges of anode vanes 17. Thus, each vane 22 abuts against one of the vanes 17 when tube 19 is inserted in the subassembly of parts 19, 20 and 22 of resonant cavity or circuit 18. With tube 10 in place, top wall 19 is positioned to complete the resonant system, and the device may be operated in any desired manner conventional with multi-cavity magnetrons.

The seal between each of the anode vanes 17 and insulating member 15 is located closely adjacent to the inner ends of vanes 17 which are in the interaction region Within the envelope. During operation, a standing wave is established along the anode vanes 17 and extension vanes 22. The voltage and current distributions of this standing wave are shown by the solid and dotted curves, respectively, in Figure 1. A point of maximum voltage and a current node (zero current) occur at the inner edges of the anode vanes 17. By locating each of the vacuum seals closely adjacent to and substantially at a current node, minimum power losses occur at the seals. As a consequence harmful heating of the seals which may destroy them is avoided. With the standing wave shown in Figure 1 the total radial length of the vanes 17 and 22 is less than a quarter wavelength. It can be seen that the radial length of the anode vanes 17 is short compared to a quarter wavelength.

Inasmuch as all but the tips of anode vanes 17 are outside of the vacuum enclosure, cooling of the anode structure may be readily accomplished. Furthermore, by varying the size of the resonant circuit 18 different frequency band widths maybe selected over which the device may be tuned. Capsule or tube 10, as is clearly apparent, may be plugged into the resonant circuit having the desired frequency response and may be removed from one circuit and inserted in another. It is further readily seen that such devices constructed in accordance with my invention embody flexibility of use to a high degree. It should be understood that the devices shown hereinwith four vanes in a radial array arethus shown by way of:

illustration and may, of course, be constructed with any desired number of vanes and spacing therebetween.

As pointed out hereinabove and as shown in the drawing, there is a standing wave established along the vanes.- By locating the point of. contact between each of the vanes 17 with its corresponding vane 22 closely adjacent to and substantially coincident with a current node of the standing wave, losses at the contacts can. be minimized so that simple face-to-face contact between the edge surfaces of. the contacting vanes will be suflicient to establish the desired electrical connection. This arrangement is shown in Figure 3, in which the multicavity magnetron includes capsule or tube 26 in which anode elements 27 are sealed along their length through envelope member 15 as shown and described in connection with Figure 1. Elements 27 are each stubs having only a small portion thereof protruding exteriorly of member 15. In this instance the tube 26 is associated with a cavity resonator 25 comprising radial extension vanes 28 which correspond to vanes 22 shown in Figure 1. The extension vanes 28 are provided with at least one pair of straps 28a and 28b, similar to the straps 17a and 17b of Figures 1 and 2. The arrangement shown in Figure 3 has an important advantage over that shown in Figure l in that, to the extent that the total radiallength of the anode elements and extension vanes deter mines the upper frequency at which such devices may be operated, device 26 (Figure 3) is considerably moreflexible. The substantial reduction in the fixed length of the anode elements sealed through the envelope makes it possible to utilize device 26 in a resonant system hav-' ing a substantially higher upper frequency limit.- In device 26 both the outer edge" or contact surface of each of elements 27 and the seal between each of elements 27 and envelope member 15 are located closely adjacent to the inner edge portions of elements 27 and substantially at acurrent node of the standing wave, as.

shown by the dotted curve 1 in Figure 3. The radial lengthof the elements" 27 may readily be such that the combined radial length of elements 21 and vanes 28 may be made very small, thus reducing the inductance of the resonant cavity to avery low value, with the consequence that the upper limit of the frequency of operation may be made very high. Further, with the straps thusconnected to vanes 28 they are replaced when the resonant circuit elements are replaced. As a result, the straps may be readily designed to give optimum, performance-with the cavity to which they are attached. The tube 26 may be-inserted into the resonator 25 from above as shown in Figure 3.

Still another formwhich my. invention may take is illustrated in Figure 4. Here the anode elements are in the formof wire or rod-shaped, anode members 29. Turned over end portions of each anode member 29 are sealed through envelope member 15. The ends of each anode member 29 which protrudesli'ghtly through member 15 are each in end to end contact with rod-shaped extension members 30, 30' which in turn are connected to side wall 20 to complete the resonant system; Preferably, strapping rings31 and 32 are applied to the radially inward ends of members 30, 30. as shown in Figure 4. In operation in the resonant system each set of .members 30, 30' and 29 function as a single anodevane. By utilizing rod-shaped anode members 29, the seal through envelope member 15' is substantially simplified- From the foregoing it is apparent that I have provided a multi-cavity magnetron and an independent capsule or tube for such devices which is highly flexible in use. While I have described my invention in detail with respect to the devices shown by way of illustration, I do not desire to be limited to the exact construction set forth, but desire to claim all modifications thereof that come within the appended claims.

What I claim is:

l. A multi-cavity magnetron, comprising an inner electron tube structure, said electron tube structure comprising an evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said member, a cathode disposed in said envelope coaxial with said members and supported between said end walls, a plurality of spaced apart anode vanes each sealed through said dielectric member with one edge thereof inside said envelope and substantially at the inner surface of said dielectric member whereby said seals are located substantially at a current node of the standing wave on said vanes during operation of said magnetron, and a cavity resonator surrounding said tube structure and comprising a wall coaxial with said cathode, a plurality of vane members each joined to said wall in. spaced apart relation with one vane member for each of. saidanode vanes, each of the vane members in said cavity resonator being oriented with and extending to one of said anode vanes witheach being in edge to edge contact with the other, said anode vanes and said cavity resonator forming a resonant system.

2. A- multi-cavity magnetron, comprising an inner electron tubestructure, said electron tube structure comprising an evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said member, a cathode disposed in said envelope coaxial with said member and supported between said end walls, a plurality of spaced apart anode vanes each sealed through said dielectric member with one edge thereof inside said envelope and one edge outside said envelope, each of said vanes terminating closely adjacent and substantially at the inner surface of said dielectric member, a pair of strapping rings joined to said anode vanes on that portion thereof extending outside of saidenvelope, one of said rings being connected to alternate vanes and the other of said rings being connected to the remaining vanes, and a cavity resonator surrounding said tube structure and comprising a wall coaxial with said cathode, a plurality of vane members each joined to said wall in spaced apart relation with one vane member for each of said anode vanes, each of the vane members in said cavity resonator being oriented with and extending to one of said anode vanes with each being in edge to edge contact with the other, said anode v'anes and said cavity resonator forming a resonant system.

3. A multi-cavit'y magnetron, comprising an inner electron t'ube structure, said electron tube structure comprising' an' evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said member, a cathode disposed in said env'elope' coaxial with said members and supported between said end walls, a plurality of spaced apart anode elements each sealed along its length through said dielectric member with one edge thereof inside said envelope closely adjacent and substantially at the inner surface of said dielectric member, and a cavity resonator surrounding said tube structure and comprising a wall coaxial with said cathode, a plurality of vane members each joined to said wall in spaced apart relation with one vane member for each of said anode elements, each of the vane members in said cavity resonator being oriented with and extending to one of said anode elements with each being in edge to edge contact with the other, a pair of strapping rings joined to said vane members in said cavity resonator, one of said rings being connected to alternate vane members, the other of said rings .being connected to the remaining vane members.

4. A multi-cavity magnetron, comprising an inner elec tron tube structure, said electron tube structure comprising an evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said dielectric member. A cathode disposed in said envelope coaxial with said dielectric member and supported between said end walls, a plurality of rod-shaped anode members each having a central portion extending substantially parallel with the axis of said cathode and end portions substantially perpendicular thereto, said end portions extending through and scaled vacuum tight to said dielectric member and terminating inside and outside said dielectric member closely adjacent and substantially at the surfaces of said dielectric member, the length of said end portions being such that the ends thereof and said seals are located substantially at the current node of the standing wave established at the inner end thereof during operation, and a cavity resonator surrounding said tube structure and comprising a wall coaxial with said cathode, a plurality of alined pairs of rod-shaped extension members each joined to said wall and extending toward one of said rod-shaped anode members, one rod-shaped member of each pair being in end to end contact with one end of one of said rod-shaped anode members and the other rod-shaped member of each pair being in end to end contact with the other end of said one rod-shaped anode member, said anode members and said cavity resonator forming a resonant system.

5. A multi-cavity magnetron, comprising an inner elec* tron tube structure, said electron tube structure comprising an evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said dielectric member, a cathode disposed in said envelope coaxial with said dielectric member and supported between said end walls, a plurality of rod-shaped anode members each having a central portion extending substantially parallel with the axis of said cathode and end portions substantially perpendicular thereto, said end portions extending through and sealed vacuum tight to said dielectric member and terminating inside and outside said dielectric member closely adjacent and substantially at the surfaces of said dielectric member, the length of said end portions being such that the ends thereof and said seals are located substantially at the current node of the standing wave established thereon during operation, and a cavity resonator surrounding said tube structure and comprising a wall coaxial with said cathode, a plurality of alined pairs of rod-shaped extension members each joined to said wall and extending to ward one of said rod-shaped anode members, one rodshaped member of each pair being in end to end contact with one end of one of said rod-shaped anode members and the other rod-shaped member of each pair being in end to end contact with the other end of said one rodshaped anode member, a pair of strapping rings joined to said rod-shaped extension members in said cavity resonator, one of said rings being connected to alternate extension members at one end of said resonator and the other of said rings being connected to the remaining extension members at said one end of said resonator, said anode members and said cavity resonator forming a resonant system.

6. An electron tube forming the interaction region of a multi-cavity magnetron for operation over a band of frequencies having a predetermined upper limit and comprising an evacuated envelope including a tubular dielectric member and a pair of end Walls sealed vacuum tight to opposite ends of said dielectric member, a cathode disposed in said envelope coaxial with said dielectric member and supported between said end walls, a plurality of spaced apart anode vanes each sealed through said dielectric member and forming a radial array with one edge thereof inside said envelope and one edge outside said envelope, each of said vanes terminating at its inner edge closely adjacent and substantially at the inner and outer surfaces of said dielectric member, said anode vanes each being short compared to a quarter wave length of said upper frequency limit.

7. An electron tube forming the interaction region of a multi-cavity magnetron for operation over a band of frequencies having a predetermined upper limit and comprising an evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said dielectric member, a cathode disposed in said envelope coaxial with said dielectric member and supported between said end walls, a plurality of spaced apart anode vanes each sealed through said dielectric members and forming a radial array with one edge thereof inside said envelope and one edge outside said envelope, each of said vanes terminating closely adjacent and substantially at the inner and outer surfaces of said dielectric members, a pair of strapping rings joined to said anode vanes on that portion thereof extending outside of said envelope, one of said rings being connected to alternate vanes and the other of said rings being connected the remaining vanes.

8. A multi-cavity magnetron comprising an inner electron tube structure, said electron tube structure comprising an evacuated envelope including a tubular dielectric member and a pair of end walls sealed vacuum tight to opposite ends of said member, a cathode disposed in said envelope coaxial with said members and supported between said end walls, a plurality of spaced apart anode elements each sealed at least at the ends thereof through said dielectric member with one edge thereof inside said envelope and substantially at the inner surface of said dielectric member whereby said seals are located substantially at a current node of the standing wave on said anode elements during operation of said magnetron, and a cavity resonator surrounding said tube structure and comprising a wall coaxial with said cathode, a plurality of vane members each joined to said wall in spaced apart relation with one vane member for each of said anode elements, each of the vane members in said cavity resonator being oriented with and extending to one of said anode elements with each being in edge to edge contact with the other, said anode elements and said cavity resonator forming a resonant system.

References Cited in the file of this patent UNITED STATES PATENTS 2,417,789 Spencer Mar. 18, 1947 2,444,419 Bondley July 6, 194 2,452,272 Tiley Oct. 26, 1948 2,553,425 Schmidt May 15, 1951 2,595,652 Fisk May 6, 1952 OTHER REFERENCES A. I. E. E. Technical Paper 52-66, December 12, 1951 (Figs. 2 and 3 and pp. 5-6) 

